During a semiconductor fabrication process, before forming semiconductor devices on a wafer, a layout design of the wafer is necessary to divide the wafer into a plurality of dies and a plurality of scribe lanes among adjacent dies. The dies are used to subsequently form the semiconductor devices; and the scribe lanes are used as cutting lines when the dies are packaged after forming the semiconductor devices.
Dividing the surface of the wafer into the dies and scribe lanes is often achieved by transferring patterns on a mask of a photolithography process to the surface of the wafer. Specifically, the process for dividing the surface of the wafer into the dies and the scribe lanes includes forming a photoresist layer on the surface of the wafer by a spin-coating process; installing the wafer having the photoresist layer into an exposure apparatus after baking the photoresist layer; exposing the baked photoresist to transfer the patterns on the mask to the photoresist layer by an exposure process; post-baking the exposed photoresist layer; and developing the post-baked photoresist layer to form the patterns in the photoresist layer. In the design of the mask for dividing the surface of the wafer into the dies and the scribe lanes, it is common to form the required patterns of the photolithography process, such as alignment marks and overlay marks, etc., in the scribe lanes.
For the existing techniques, the photoresist often has offset, rotation, shrinking and extending, and/or orthogonal change, etc., during the overlay exposure process because of the overlay precision, wafer shift and focusing precision, etc. Thus, an overlay measuring mark is required for measuring the exposure error between different dies formed in a same photoresist layer, and/or the exposure error between the dies at a same position of different photoresist layers. By doing so, the overlay precision of the wafer is obtained.
However, for the overlay marks formed at a same position of different photoresist layers, there is a resolution difference. Such a resolution difference affects the detection of the overlay precision. Thus, the overlay marks may be unable to meet the requirement of the continuous development of the manufacturing. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems in the art.